Investigate trisomy in chromosome 18

You are asked to investigate whether a cell has trisomy in chromosome 18. Describe briefly the experiment (method) you would perform (use) to show whether the cell has trisomy for chromosome 18. Assume you have a sample of blood from the patient you are going to analyze.

We will isolate white cells from the patient's blood and grow the isolated cells in culture in culture medium for 48-72 hours and arrest cells in mitosis by treating them with colcemid. Then we will use a method of chromosome analysis like "chromosome in situ hybridization" in which DNA will be denatured and a labeled probe will hybridize on the denatured chromosomal DNA.
Another chromosome analysis method that can be used is chromosome painting.